Just three weeks before NYU’s newest class moves into the area, a group of junkies and crackheads has turned a leafy pathway in Washington Square Park into an open-air drug den — and the NYPD is doing nothing about it.

As many as 20 strung-out vagrants have taken over several benches in the park’s northwest corner, where they openly consume hard drugs just steps from the children’s playground, outraged neighbors said.

One Village resident who walks his dog through the park daily said he has repeatedly witnessed people blatantly smoking crack — and even saw one man use a handheld mirror to inject narcotics into a vein in his neck as two cops sat in a cruiser about 15 feet away.

“I dunno if they have a Twitter feed or what, but the word is out and the numbers get bigger by the day,” said the resident, a 33-year-old property manager.

“I’ve lived by the park seven years and I have never in my life seen someone shooting heroin in the middle of broad daylight, literally surrounded by pedestrians enjoying an afternoon outside.”

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No cops were stationed inside the park Thursday, but at one point, two officers pulled up in a patrol car and parked at Washington Square North to eat ­salads in their vehicle.

Asked why they weren’t cracking down on the lawlessness within their sight, one cop said: “We aren’t even here for that specifically. There’s a unit that’s dealing with all of that. I can’t say more than that.”

They left about 10 minutes later.

An NYPD spokeswoman, Sgt. Jessica McRory, said: “The precinct has received complaints in regards to that area of the park. We currently have officers assigned to that area.